1. Field of the Invention
The invention relates to dynamic random access memory (DRAM), and more particularly, to a checkerboard trench DRAM.
2. Description of the Prior Art
Electrical products are becoming lighter, thinner, shorter, and smaller, and dynamic random access memory (DRAMs) geometries are being scaled down to match the trends of high integration and high density. In a conventional planar trench capacitor DRAM, a source, a gate, and a drain of a MOS transistor are horizontally positioned on a surface of a substrate. This is an important factor affecting a design of a size of transistors in the DRAM. Therefore, vertical transistors are used in trench capacitor DRAMs.
Generally speaking, fabrication of a vertical transistor structure involves etching the substrate for producing a deep trench, fabricating a trench capacitor in the deep trench, forming a vertical transistor near the trench capacitor, and locating the drain, gate, and source vertically to decrease a horizontal area of the transistor substantially and increase semiconductor component integration.
A length and a width of the gate channel are important factors that affect an efficiency of the vertical transistor in a vertical transistor trench capacitor DRAM. The length of the gate channel decides a channel length, along which electrons pass from the source to the drain. The width of the gate channel decides a number of electrons that pass from the source to the drain. If the length of the gate channel can be shortened in the vertical transistor trench capacitor DRAM, a leakage of the transistor will be decreased significantly, and the efficiency of the vertical transistor trench capacitor DRAM will increase.
Industry research has produced a checkerboard trench-DRAM. One transistor matches with a corresponding trench capacitor in the checkerboard trench-DRAM. It is suitable for 90 nm manufacture in order to improve planar standard manufacture, and to achieve satisfactory capacitances without needing to use a high dielectric material. If a vertical transistor with a shorter gate channel length could be fabricated, the leakage current effect of the transistor could be decreased. And applying the vertical transistor to the checkerboard trench DRAM could greatly increase the effectiveness of the checkerboard trench DRAM. Thus, developing a vertical transistor with a short gate channel length is an important objective of the semiconductor industry.